As a media-agitation type pulverizer, there has been known a media-agitation (agitated media) mill proposed in JP 2005-199125 A.
The media-agitation mill proposed in the JP 2005-199125A comprises a pulverization tank including an end plate closing up an upper end thereof and internally having a pulverization chamber containing pulverizing media, a rotary shaft rotatably provided in the pulverization tank, and an agitating/separating member provided on a portion of the rotary shaft located inside the pulverization chamber and adapted to be rotatable integrally with the rotary shaft. This media-agitation mill is characterized in that an inner wall surface of the pulverization chamber and an outer peripheral surface of the agitating/separating member are formed in shapes conforming to each other, wherein the media-agitation mill further comprises a separation/discharge passage extending from the outer peripheral surface to penetrate through a central portion of the agitating/separating member and then extending from the central portion of the agitating/separating member to penetrate through a central portion of the rotary shaft and communicate with an outside of the pulverization chamber, and a pressure relief hole penetrating between upper and lower surfaces of the agitating/separating member in an axial direction of the rotary shaft to provide communication between upper and lower regions of an inside of the pulverization chamber.
However, in the media-agitation mill having the above structure, the pulverizing media are liable to be concentrated around a maximum-diameter portion where a centrifugal force is maximized, i.e., to be localized in a specific position, so that a dispersion or pulverization force varies with position, and the variation is large. Thus, there is a problem that a raw material is not uniformly dispersed or pulverized, causing difficulty in obtaining a high-quality product.
Therefore, the applicant of this application proposed a media-agitation type pulverizer capable of obtaining a high-quality product by a good pulverizing/dispersing action, in JP 2009-103529 (JP 2010-253339A).
The media-agitation type pulverizer proposed in the JP 2009-103529 comprises: a pulverization container having an upright cylindrical pulverization chamber containing pulverizing media in the form of beads; a raw-material-slurry supply port provided in the pulverization container; an agitating member disposed in a bottom region of the pulverization chamber and having a rotary shaft substantially coaxial with a central axis of the pulverization chamber; and a media separation member provided within the pulverization chamber and above the agitating member. This media-agitation type pulverizer is characterized in that it further comprises a guide ring installed to radially divide a lower region of the pulverization chamber into an inner section and an annular outer section, wherein an upward flow path of a mixture of the pulverizing media and the raw material slurry is created in the outer section of the lower region of the pulverization chamber.
In the media-agitation type pulverizer proposed in the JP 2009-103529, the guide ring is installed in the pulverization chamber, as mentioned above, whereby a flow of the mixture of the pulverizing media and the raw material slurry can be formed as a combined flow (i.e., helicoidal (spiral or helical) flow) consisting of a flow moving in a circumferential direction of the pulverization chamber (i.e., a primary flow) and a flow capable of regularly repeating a movement cycle of, after moving in a radially outward direction of the pulverization chamber toward an inner wall of the pulverization container, moving upwardly through the upward flow path between the guide ring and the pulverization container, and then moving downwardly from a central region of the pulverization chamber to return to the agitating member, via a space inward of the guide ring (i.e., a secondary flow). Thus, even if a volume ratio of beads to the pulverization chamber is relatively low, localization (uneven distribution) of the pulverization media can be suppressed to some extent to provide enhanced pulverization/dispersion efficiency.
However, the helicoidal flow formed by the media-agitation type pulverizer proposed in the JP 2009-103529 is unstable due to weakness and instability of the secondary flow thereof, so that centrifugal force distribution is likely to become uneven, which causes localization of the pulverization media in the helicoidal flow. Thus, there is a problem of non-uniform pulverization and not-so-satisfactory energy efficiency.